A Tidewater employee said ratchets used to hold the barge in place appeared to have been intentionally loosened, according to a Coast Guard news release. A longshore union spokeswoman said the union had nothing to do with it.

"If in fact it was intentional, that's an extremely serious act of recklessness," said Capt. Bruce Jones, commander of the Coast Guard's Columbia River sector. "It could have endangered a lot of people or caused a collision or resulted in some environmental damage."

The fact that Barge 550 was loaded with grain destined for the locked-out elevators is also significant because it shows that tugboat companies have found a way around longshore picket lines. Columbia River tugs are typically crewed by union members affiliated with the International Longshore and Warehouse Union.

Until recently, two Portland and Vancouver grain terminals that have locked out longshoremen in a yearlong labor dispute had received grain solely by rail. But now, Tidewater and Shaver Transportation Co. deliver barges to two staging areas, where grain-elevator companies arrange to retrieve them.

Coast Guard officials said they didn't know whether Tidewater originally intended to deliver Barge 550 to United Grain Corp. in Vancouver or Columbia Grain Inc. in Portland. A Tidewater spokeswoman did not return calls for comment Monday.

The barge was found floating near the navigation channel used by large vessels, according to the Coast Guard, which is responsible for policing shipping channels.

"Intentionally causing damage to a vessel or its cargo is a crime punishable by a fine and imprisonment for up to 20 years," the Coast Guard release said.

Coast Guard officials said anyone with information about the incident should contact Sector Columbia River Command Center watchstanders in Warrenton at 503-861-6211.

Jennifer Sargent, a longshore union spokeswoman, said strikebreaking companies often try to malign workers during labor disputes. "The manner in which the barge broke free from the dock ispure speculation until the investigation concludes," Sargent wrote in an e-mail, "and the employer'sprivate security and strikebreaking firm should be as closely examinedas anyone else during that process."

Sargent noted that last week, a Clark County prosecutor declined to press charges against Vancouver longshore local official Todd Walker, who was accused by United Grain in March of sabotaging operations at the terminal. The prosecutor concluded that the company's video failed to prove a crime had occurred, she said.

"The company had used that one fabricated allegation to justify locking out an entire local workforce," Sargent said.

But Pat McCormick, a spokesman for the grain handlers, said Monday that, "We remain convinced the the video evidence shows Mr. Walker attempting to sabotage critical operating equipment last December, and the civil case against Mr. Walker will now move forward...."